How to construct a punnett square

• Our genes are inherited from our parents, and the different combinations of these genes make us unique
• Genetic inheritance controls the characteristics of all living things
• Genetic inheritance includes:

  • Carrying out a genetic cross
  • How to construct Punnett squares
  • Examples of genetic crosses
  • Sex determination
  • Inherited disorders
  • Limits of genetic testing
  • Family trees
  • Understanding of genetics including Mendel's work
• Method to construct Punnett squares:

  • Determine the parental genotypes - the allele combinations for the male and female
  • Split the alleles for each parental type and add them into the Punnett square around the edges
  • Work out the new possible genetic combinations inside the Punnett square
  • Use this information to answer questions related to allele combinations in the offspring, calculate probability ratios, or determine the phenotypes of the offspring
• Example:

  • Inheritance of fur colour in mice is controlled by a single gene
  • White fur is recessive, grey fur is dominant
  • When two mice that are heterozygous for the fur colour gene mate, there is a 75% probability that the offspring will have grey fur and a 25% probability that the offspring will have white fur